The present invention relates generally to, inorganic coating materials, and more particularly to using an inorganic coating material for forming coated film electrical insulation.
Conventionally, most coating materials are made from organic polymers and organic solvents, which may undesirably result in contamination of the atmosphere, water, soil, and the like. Disposal and handling of organic compounds has long been a problem from the viewpoint of environmental protection.
The trend in recent developments of technology related to commonly used coating materials of inorganic substances is to use mainly silicon oxide with natural quartzite as a starting material.
For example, a mixture of an alkali silicate and a carbonate is fused at a high temperature and then passed through a hydrothermal reaction to form a water-soluble silicate. A coated film is formed by a water-insolubilization reaction of alkali metal ions and a self-condensation reaction of silicate ions.
Furthermore, it is necessary that this coated film be baked at a high temperature (300xc2x0 C.). Moreover, by a method for ion exchange of the alkali silicate like this in order to carry out the removal of alkali metals, a coating material consisting of colloidal silica can be obtained. This colloidal silica will supplement the low water resistance of a coated film of alkali silicate. However, in practice, adherence characteristics and skin film strength are insufficient. Reinforcing materials like metal fiber mica are used in combination.
In addition to the coating materials of pure inorganic substances like these, there are also coating materials of organic-inorganic hybrid systems. However, in the field of coating materials as a whole, a combination is used in practice only about 1% of the time. Although there are problems in production technology in the prior art, the most important consideration is reliability with respect to adherence on the material coated. In particular, for ceramics having SiO2, Al2O3 and other oxides having heat resistance and high electrical insulating characteristics, adherence onto metals has always been considered to be questionable.
On the other band, technology in regard to inorganic compositions with high insulating characteristics has been upgraded by aiming at improvement in heat resistance and improvement in adhering capability with respect to the objects to be adhered or bonded.
Incombustible coating materials for use in electronic parts have been disclosed, for example, in Japanese Kokai Patent Application No. Sho 62 [1987]-25686. Binders by the combination of curing type inorganic compositions have been proposed as heat-resistant inorganic coating materials, heat-resistant agents, and so on in Japanese Kokai Patent Application No. Hei 1 [1989]-239049. Furthermore, an inorganic composition with electrical insulating characteristics has been disclosed in Japanese Kokai Patent Application No. Hei 3 [1991]-74483.
The present invention is directed towards providing an inorganic coating material that maintains the properties of high heat resistance and high electrical insulating characteristics of inorganic materials, while enhancing excellent adhesion with respect to an object to be coated. A water-based suspension state with a specific gravity in the range of 1.5 to 2.5 is obtained by using as major raw materials at least two types of metal oxide particles having heat-resistant characteristics at temperatures above 1000xc2x0 C., distributing diameters of these particles in the range of 0.1 xcexcm to 30 xcexcm, adjusting the average value of their particle diameters to 0.2 xcexcm to 0.8 xcexcm, and adding water and stirring.